Automatic inspection of printing plates or cylinders

Abstract

A method for inspecting a surface of a printing medium, the method comprising the steps of acquiring an image of the surface or a portion thereof, digitizing the acquired image whereby a digitized real representation of the surface or portion is obtained. The method also include the step of for each of said digitized real representation performing either or both of the steps of comparing said digitized real representation with a digital reference representation, said reference representation being a virtual digital fault-free representation of said surface or portion thereof and determining whether said real digitized representation is in compliance with stipulations of a set of rules which define the characteristics of a fault-free digital representation of said surface or portion, and providing either a correct indication output signal where there is a match between said real digitized representation with said reference digital representation in the case of the step of comparing or compliance with said rules in the case of said step of determining, or fault indication output signal where there is a mismatch in the case of the step of comparing or incompliance in the case of the case of determining.

Description

The present invention relates to a method and system for the inspection of a printing plate or cylinder, in order to automatically detect errors and defects which may influence the quality of the print.Books, magazines and other publications are typically produced by offset or gravure printing. In offset printing, a plate is imaged in a contact frame or by direct exposure to a laser beam. The plate is later mounted on a press and then impressed on the printed substrate. In gravure printing, a cylinder is engraved by laser exposure and subsequent chemical etching or by the use of a penetrating pyramid shaped diamond stylus in an apparatus known as a "helioklischograph".The formation of the printing plate for offset printing or the cylinder for gravure printing, is error prone and very often defects occur. Such errors may arise from a number of sources. In offset printing the plates are routinely imaged in vacuum contact frames or Step and Repeat machines such as Impomaster.TM. (manuf...

AI Technical Summary

Benefits of technology

The present invention provides a novel method for inspection of a surface of a printing medium, e.g. a printing plate or gravure cylinder. In accordance with the present invention an image of the printing surface is optically acquired, a real digital representation of the surface is produced and a computer then determines whether the real digital representation has a defect or not and provides an o

Problems solved by technology

The formation of the printing plate for offset printing or the cylinder for gravure printing, is error prone and very often defects occur.

Such errors may arise from a number of sources.

If air pockets (or dust particles) remain between the film and the plate, the exposed image will have non-uniform areas.

In addition, errors in plate exposure may be caused by scratches, dust and paper/cloth lint that remain on the film after cleaning.

However, errors in imaged areas and errors related to separation or imposition order cannot be corrected at all.

One source of defects in the manufacturing process of gravure cylinders is faults which occasionally occur in the stylus, e.g. a chopped tip, stylus rib defects and others which may be caused, for example, by stylus material fatigue, rib wearing, etc.

In addition, abnormal gravure cells are formed at times by inaccuracies in the current which drives

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